1. Field of the Invention
The present invention relates to an image communication apparatus, such as a facsimile apparatus.
2. Description of the Related Art
In general, a facsimile apparatus counts the number of error lines each time one page of data has been received. If the number of error lines is equal to or smaller than a preselected number, the facsimile transmits, responding to a Q command, a signal MCF which indicates that the image signals have been safely received so that the facsimile apparatus is ready for receiving the data of the next page. When the number of the error lines exceeds the preselected value, the facsimile apparatus transmits, responding to the Q command, a signal RTP which indicates that a retraining is necessary for the receipt of the next page although the image signals have been safely received or, alternatively, a signal RTN which indicates that the image signals could not be received safely so that retraining is necessary for the receipt of the next page. Transmission of the signals MCF, RTP or RTN must be done within a predetermined period from the receipt of the one page of data.
Hitherto, printers of the type employing thermal heads were broadly used as the recording means of facsimile apparatuses. Typically, the thermal printer used in facsimile apparatuses is a line printer having a thermal head which is sized to cover one full line of recording so as to perform recording in line-by-line fashion. In addition, the time required for completing one line of recording is shorter than the minimum transmission time for transmission of one line of data. This type of printer, therefore, can record the decoded data instantaneously, as well as responding in time to the Q command.
In recent years, however, there has been an increasing demand for facsimile apparatuses which use ordinary or plain paper sheets in place of conventionally used thermal recording paper sheets.
Laser beam printers (referred to as "LBP" hereinafter) are commonly used as the recording devices of facsimile apparatuses for recording data on plain paper sheets. An LBP performs printing on a page basis due to characteristics of its recording operation, so that the time required for completing recording is constant regardless of the volume of data contained in each page. In operation, recording is commenced after completion of receipt of one page of data to be printed, and the above-mentioned constant time is required for completing the recording. This requires that the facsimile apparatus as a system has a receiving page memory which is capable of storing coded data of a plurality of pages. In addition, it is necessary to employ two different decoding means: one for counting error lines and one for decoding the received data, in order to improve the response to the Q command and to realize real-time recording, i.e., recording while receiving. Each of these two decoding means employs an exclusive and expensive logic circuit, in order to achieve real-time processing, even in low-price versions of facsimile apparatuses.
The ink jet recording method also is known as a method for recording data on plain paper sheets. This recording method generally employs a block printer which performs printing of several lines at a time, requiring a longer time for completing the printing than the foregoing two types of printers. Use of this type of printer in a facsimile apparatus, therefore, essentially requires two different decoding means as in the facsimile apparatuses having LBP printers, in order to ensure that the response to the Q command is done without fail and in order to realize "recording while receiving".
An LBP is composed of a record control section which controls the recording operation and an interface control section which performs the control of an interface between the LBP and a computer. These two control sections are realized by different and discrete hardware, for the reasons stated below. The control of the recording operation in the LBP is complicated so that capacity of the CPU is almost fully occupied by the recording control function, particularly when a processing unit having low cost performance s used as the CPU. On the other hand, the interface is required to adapt to various computers produced by various manufacturers and, therefore, is preferably designed for various computer specifications of different computer manufacturers, independently of the recording control section, i.e., without affecting the recording control function. Such an interface design is beneficial both to the LBP manufacturer and the computer manufacturers as purchasers. Therefore, when an LBP is considered as the recording device of a facsimile apparatus, the interface control section of the LBP is designed to adapt to the specific signal form of the facsimile apparatus. For instance, formation of font data based on character codes is essential when an LBP is used as an output terminal of a computer, whereas, when the LBP is used in a facsimile apparatus, such formation of font data is not necessary but a function is required for recording image based on image data. A facsimile apparatus having an automatic receiving function also requires a signal indicative of a shortage of the recording medium such as toner.
Meanwhile, a printer of the type known as the ink jet printer has been noticed as being promising because It can have a reduced size and can be produced at low cost as compared with LBPs. In one type of such an ink net printer, thermal energy is applied to cause a change in the state of the ink so as to form an ink droplet, thereby recording data on ordinary or plain paper sheets. As in the case of an LBP, the ink jet printer also has two control functions: a function to control the recording operation and a function to control the interface. In the case of ink jet printers, however, these two functions are realized by a single CPU, because the ink jet printers are inherently designed for low cost and small size and because the requirement for high speed of recording control is not so strict as compared with LBPs.
Adaptation of an ink jet printer to facsimile apparatuses would be possible simply by modifying the interface control function alone in conformity of the specifications of the facsimile apparatuses. Such modification, however, is inevitably accompanied by an undesirable effect on the recording control function, when both the recording function and the interface function are under the control of a common CPU. In general, an ink jet printer is usually designed to be just enough for the required functions, in order to reduce the cost of production and, therefore, the number of the input/output ports also is limited to make it difficult to add to the ink jet printer additional functions for production and transmission of a signal indicative of shortage of ink, a signal indicative of completion of the recording operation, and so forth.